Method of and means for broducing metallized surfaces on rubber compounds containingsulphur



rarefied Feb. 24, 1925.

W {T ED a ALBERT IVAN GATES WARREN, F CATEltHAM VALLEY, SURREY, ENGLAND,

SIGN'OR TO CATERI-IAM WORKS LIMITED, 013

ISTERED UNDER BRITISH LAW.

Mm. :1. a corrranr asse METHOD OF AND MEANS FDR BRODUCING METALLIZEDSURFACES 0N BEER COMZPOUINDS CONTAINING SULPR.

No Drawing.

5 House, 37 5 Croydon Road, Caterham Valley,

county of Surrey, England. have invented a new and'useful Method of andMeans for Producing Metallized Surfaces on Rubber Compounds ContainingSulphur, of which the following is a specification.

This invention relates to the production. of metal surfaces on rubbercompounds containing sulphur such as vulcanite or ebonite, or onsubstances consisting of admixtures of materials but in which rubbercontaining sulphur predominates.

It is well known that such materials as ebonite and vulcanite in theirraw or finished state have but small affinity for chemical 2 changeunder ordinary conditions of temperature and use and for this purposeare often deliberately chosen for many industrial applications.

In the present invention advantage is taken of the fact that the sulphurpresent in the rubber compound is capable under given conditions of heatand time of combining with metals or metallic salts when in intimatecontact therewith, the metal or positive radicle of the salt beingabsorbed as a sulphide or analogous compound of.

sulphur, this combination being determined 'in its area by directcontact with the metal or metallic salt, and hits depth depending uponthe length of' time durin which contact is preserved over the criticaltemperature, and in the .case of metallic salts the duration of hotimmersion, the thickness of deposit, and subsequent heat soaking 40process.

This metallic absorption is evidenced b the formation of metallicsulphides whic become apparent in, and upon the external or skin-surfaceof the article treated. A0-

cording to this invention the article is then subjected to a suitabledecomposing agent to eliminate the sulphur radicle and leave aconducting surface upon which if desired electrodeposltion of othermetals can be madethereafter in any known manner.

The metals preferably employed for this foil.

Application filed December '5, 1922. filerial No. 605,072.

contacting rocess are gold and silver or Y a mixture t erect or theirsalts or oxides, but most of the metals capable of forniin sulphides orcompounds with sulphur suc as zinc, nickel I and tin may be employed.though the results of their use are neither so certain, reliable ordesirable as is the case with gold or silver.

In operation and in the preferred form h of carrying this invention intoefiect, the article to be manufactured (other than plates, sheets or thelike fiat surface articles) is determined in shape by a mould or matrix.Into this mould a metallic foil consisting of (35 a mixture of gold andsilver is inserted, the gold constituent being preferably from 10-25 ercent and the silver constituent prefera ly 90-75 per cent, dependin uponthe final surface of the article required. The foil is of but smallthickness varying from 1/1000 to 1/20" in thickness, depending upon themass or pattern of rubber-sulphur material with which it will contact.In an case'the foil is by tooling, pressing, moul ing or like mechanicalmeans forced into intimate contact with the mould, and caused closelyto. engage the surfaces presented. The unvulcanized or partly'vulcanized rubber-sulphur material is now pressed into engagement withthe foil, care being taken that no air bubbles or articles of foreignmatter are interposed tween the two engaging surfaces, therubber-sulphur mass completely filling the foil-faced mould. Pressuremay be employed to ensure contact, but a rolling or pugging action ismost beneficial for the purpose, or the mould may be placed under vacuumto remove air bubbles between the rubber material and the The articlesin contact in the mould are now placed in an apparatus and heat treatedto a yulcanizing temperature, name= ly between 300 to 330 F. for aperiod of at least 60 .minutes. The temperature and period of heatingdepend in some small measure upon the quality of rubber used and theextent of prior partial vulcanizations and may vary withinreasonablelimits. It is preferable, therefore, first to ascertain by experimentthe actual temperature and period of heating required for each distinctcontiguity. stripped. At this stage the metalhzed and kind ofvulcanizable rubber. When the foil covered mass is extracted from thevulcanizer, it is found that the foil in contact may easily be removedfrom the vulcanized article, and that an appreciable loss in weight offoil has taken place, the loss being accounted for by its absorptionwithin the mass, and is evidenced as 'a sulphide or like sulphurcompound of the metal in recent The remaining foil is now required for a5 volt difference of potential' The bath must be made of a saturatedsolution of ammonium nitrate crystals at 65 F. When the article sotreated is removed an obvious metallic surface is apparent. This surfaceis then burnished with a fine scratch brush and is then ready for use,or can be thickened with a depositable metal. If copper cyanide isemployed an electrolytic bath is prepared, on a basis of 8 ozs. Coppercyanide crystals to one gallon of water at (55 F and after immersion ofthe article as the cathode for ten minutes or less at a difference ofpotential of 2-3 volts it is found that the sulphides are reducedleaving a metallic surface with traces of copper. If an entirelycoppered surface is required it may be obtained by longer immersion inthe same, or for economy and a very smooth coating it may be inserted inan electrolytic copper sulphate bath composed of 1 lb. of coppersulphate to the gallon and i oz. of sulphuric acid at 65 F. and pressureof 5.: volt.

This process of reducing or decomposing to a metallic state the surfacemetallic salt, is of prime importance as otherwise stripping of theelectro-deposited layer will ensue sooner or later, or the metallayersubsequently deposited will blacken or ultimately show traces ofsulphur activity.

When metallic salts in lieu of foil are employed, the article made ofrubbercompound may be first moulded and vulcanized or partly vulcanized.The moulded article after the first vulcanization has the appearance ofvulcanite or ebonite depending upon the rubber compound employed that isto say it is a definite stable article in its moulded form. It is now,after being cooled, coated with a metallic salt or oxide preferably asalt or oxide of silver or gold or a mixture thereof. Again, preferablythe oxide of silver (Ag O) is employed and this must be careful yrepared for purity and be of very fine division. by forming same into aliquid or paste, with a volatile medium such as chloroform and/orrectified spirits of tur entine. This preparation may be applied byspraying or painting, or the article if wholly to be coated may bedipped into the preparation. After a sufficient coating has been appliedto that portion ofthe article to be metallized, the volatile constituentis'allowed to but such classes are well known in the art and are easilyobtainable.

It is found that the further vulcanization has the result oftransforming the metallic salt or oxide applied into a sulphide so thatafter the article is removed from its heat treatment the silver oxideand/or gold salt has become chemically combined with the surface depthof the rubber compound, as a sulphide or analogous sulphur salt. Furtherdecom osition of the sulphide may now be efiected as previouslydescribed by placing the article in an electrolytic bath of ammoniumnitrate or copper cyanide solution and this process of further reductionand decomposition herein termed metallization may in fact be carried outsimultaneously with the process of plating, in case of the coppercyanide bath.

Alternatively original moulds may be coatel with metallic salts oroxides in paste form prior to the first moulding operation in which casethe moulded article after vulcanization has all the characteristics ofmetal absorption, as though a metal foil has been employed, theproduction of a metallic surface for later electro-deposition being madein themanner set out above. In all cases, care must be taken thatsurface sulphides produced in the heat treatment are reduced or as alast precaution removed mechanically as with the scratch brush be foreplating takes place, or the later do position will be unsatisfactory andproduce uneven surfaces which are not desirable, the

' object being to produce a puremetallic surface on the article, whichmetallizati'on decreases in purity with depth.

It is found that when the metallic salts or oxides are applied in pasteform as above described, to either the mould or the article,

It is prepared for use.

lit)

lid

there is sumcient penetration or absorption of metal into the rubbercompound to prevent any tendency of this chemically combined layercracking oil. The metallic salt coating paste, however, must behomogeneous and of equal thickness over the portions agent similarlyemployed which will obtain the desired reduction or decomposition to ametallic surface in the final stages of metallization maybe regarded asthe chemi cal equivalent of those stated above. If reduction or decomosition takes place in the plating bath it is necessary to move thecathode clips during the process of plating along the article to beplated. so that the required action takes place with as near as possibleequal intensity over the whole area.

in cases where certain rubber masses appear to react slowly with themetallic mediurns or salts employed the formation of surface sulphidesmay be accelerated by spraying or coating the surface of the articlewith carbon disulphide and then applying the metal or metal salt.

in like manner to the use of foil, and metallic oxides or salts, finelycomminuted metallic powders may be employed, the

powder being applied either as a paste compounded with a volatilemedium, or the article to be treated may be coated with a volatilemedium and the metallic 'dust applied; or the metallic dust mayalternatively be applied to the mould, the further process ofmanufacture 'bein otherwise identical with those described a ove.

This process of metallizing rubber compounds is particularly adaptedinter alia to the production of gold covered dentures,

in the manufacture of which impressions of the mouth are taken in theusual way and moulds cast therefrom, in plaster of Paris. The mould isthen preferably lined with foil and the dental rubber inserted until thedesired thickness of plate is built up, the teeth are inserted and theuppermost surface is then also covered with foil, and

after vulcanization the denture is. removed from the mould when cold andthe foil stripped therefrom The denture is now immediately placed in theelectrolytic am monium nitrate bath as the cathode and treated for say30 seconds to 1 minute at a pressure of 5 volts, the anode being 6" awayfrom the cathode. It is now removed, then washed, and scratch brushedbeing then ready for the final gold coating. This latter is applied inan ordinary electrolyticgold salt bath at a pressure of 1 volt until thedesired thickness of gold is deposited. It

is now burnished or polished and is ready for use, the final product hasall the appearance and hygienic qualities of a gold plate without thedisadvantage of cost,

weight and liability to bend.

- I claim z--' i 1. In a process for producing a metal surface on arubber compound containing sulphur, the preliminary production of ametal sulphide on the surface by combination of a metal with the sulphurin the rubber, and subseiuently reducmg such sulphide.

2. process for producing a metal surface on a rubber compound containingsulphur, consisting of the application to the surface of the rubbercompound, of a metal, heating the body to" combine the meta and thesulphur, removal of uricombined metal, and reduction of themetalsulphide metal, and electro-depositing further metal on the metalderived from such reduction.

. 3. In a process for producing a metal surface on a rubber compoundcontainin sul phur, the production of a metal sulphide by eating thecompound in contact with the metal, and subsequently reducing the salphide to metal by electrolytic treatment.

4. A process for producin a metal sur= face on a body made of a rubbercompound containing sulphur which consists in cov erin the body withgold and silver alloy, heatmg the body to vulcanize the same and tocause combination of some of the sulphur with the metal, removal ofuncombined meta al reduction of the sulphide by treating the body in anelectrolytic bath. and electro-depositing further metal on that derivedfrom reduction.

5. In a process as claimed in claim 1, the particular method consistin'of the use of a silver oxide in a volatile m ium to produce I finelycomminuted metal powder to produce a surface layer, and subsequentlyheating to produce combination between the metal and the sulphur.

7. A process for producing a metal surface on a rubber co'm oundcontaining sulphur, consisting of t e application to the surface of therubber com ound of a metal compound, heating the be y to combine themetal and the sulphur, removal of uncombined metal, and reduction of themetal sulphide to metal, and electro-depositing further metal on themetal derived from such reduction. p

8. In a process for producing a metal surface on a rubber compoundcontaining sulphur, the production of a metal sulphide by heating thecompound in contact with the compound thereof, andsubsequently reducingthe sulphide to metal by electrelytic and reduction of the metalsulphide ix; 1.

treatment. m fll- 9. A process for producmg a metal sur- 10. An artlcleof manufacture comprising face on a rubber compound cpntaining sularubber body having metal surfaces chemphur, consisting of theappheat-ion to the lcally cpmbined therewith.

surface of the rubber con: ound of a metal, In wltness whereof I afiixmy signature.

heating the body to combme the metal and the sulphur, removal ofuncembmed metal, ALBERT IVAN GATES WARREN.

